FAQ

FAQs – General:

What is Passive Ventilation?
Simply put, Passive ventilation is a method of allowing continuous, calculated, unimpeded airflow above the thermal envelope of a building with the objective of eliminating condensation by removing warm moist air from the roof voids of wall cavities.
Why do we need to passively ventilate?
Increased focus on energy efficiency, heating and insulation has led to “tighter” building construction. As buildings become more airtight, buildings are unable to breath and expel moisture that enters the building through various means. If moisture is not expelled from the building it can lead to condensation which can be detrimental both to the building and to its occupants. The build up of condensation in a building can lead to the decay of building products and create an environment for toxic moulds to thrive.
Is it a proven solution?
Yes. Passive Ventilation has been tried and tested across Europe & USA covering the most extreme climatic conditions for decades. More recently, in 2015 Passive Ventilation was introduced into New Zealand and is now a widely accepted practice. Australia has been using different forms of ventilation however VENT Systems passive ventilation systems offer a different system of passive ventilation in so much as they are in line with NCC requirements and offer calculated, continuous and unimpeded airflow.
What is the difference between mechanical and passive ventilation and is there a need to passively ventilate a mechanical system is installed?
Many mechanical ventilation products focus mainly on the ventilation of habitable areas. It is common for many of these systems to have extraction vents in the habitable areas of the building that terminate in the roof space. The result of this is that the condensation from the habitable areas of the building are literally transferred into the roof cavity. It is imperative that any moisture has the ability to exit or escape the roof cavity. Whilst most mechanical ventilation companies offer systems that bypass the roof cavity, whilst these are preferable options, they still only deal with moisture in the habitable areas of the building. They do not deal with moisture that is created in the roof cavity itself. Leaving this moisture in the roof cavity it can very quickly create the ideal habitat for toxic moulds.
Will passively ventilating a roof cavity compromise the thermal efficiency of my insulation?
In principle, passively ventilating will not compromise the thermal efficiency of insulation. Despite reducing the air temperature above the insulation, by creating air movement and allowing moist air to escape the roof cavity, passively ventilating safeguards the thermal qualities of insulation which may be compromised should they become wet. However, as the thermal ratings of insulation will vary depending on the R-Ratings, the product supplier etc. it is always recommended to check with your insulation provider first.
Does every roof require passive ventilation?
It is our strong recommendation that every roof should be passively ventilated. This is not to say that ever roof will experience internal moisture issues, however every roof that is not passively ventilated may suffer from internal moisture issues depending on a number of factors. By passively ventilating the roof space, you mitigate the risk of being exposed to internal moisture and associated issues.
How costly is it to passively ventilate my roof space?
When compared with mechanical ventilation systems, passive ventilation is relatively cheap and inexpensive as there are no ongoing running or maintenance costs after the initial install. The installation costs themselves depend on the roof design and the product combinations required.

FAQs – Product:

Does the VENT Systems Ventilated Roof Batten - VB20 sit on the top of sarking/membrane or underneath the sarking/membrane?

When used on the roof, the VB20 can be placed on top or underneath the sarking/membrane, depending on the type of roof construction and state requirement.

Australian Standards and state requirements should always be consulted before deciding the placement of the sarking/membrane. Vent Systems provides technical drawings for both placements.

What is the gap between Vent Systems Ridge and Apron Vents and Ridge Caps, Barge or Apron Flashings?

The caps, barge or flashings sit on top of the vents. It is imperative that the capping or flashings extend 20mm beyond the ridge or apron vents to ensure that airflow out of the vents is not impeded. The aluminium flashing portion of the ridge and apron vents extends 50mm beyond the vents, aesthetically it is recommended that the capping and flashing details can be extended to cover the aluminium flashing.

What’s the deepest trough Vent Systems Ridge or Apron Vents can work on?

The RV10DT has been tested to a trough depth of 50mm. Please note however that when applying the RV10DT to a deep trough profile snipping will be required. One should take care during the application process to not force the flashing tape beyond it’s intended use, as this may cause the tape to break away from the vent.

What over fascia vent do you apply to a roof of under 15°?

The applicable standards and construction codes should always be consulted before determining the correct volume of airflow required and the applicable Over Fascia Vent. For example, in accordance with BS5250, for any traditional roof with a roof pitch less than 15° a G2500N VENT Over Fascia Vent should be applied.  In accordance with NCC 2019 Building Code of Australia, Vol 2, Part 3.8.7.4.b , Suitable for roof pitches <22° or 1/150. In accordance with Guide for Control of Condensation and Mould in Tasmanian Homes (CBOS vs 2), Suitable for roof pitches <16° or 1/150.

For any cathedral roof, irrespective of the pitch of the roof a G2500N VENT Over Fascia Vent is recommended.

The G2500N is designed to allow a calculated airflow of 25,000mm² per linear metre into the roof cavity. The smaller or tighter the roof cavity the more airflow is required.

Is it better to ventilate through the soffit or over the fascia and do VENT offer soffit strip vent in their product range?

VENT System products allow a calculated airflow into the roof cavity whether it be through the soffit or over the fascia. Over Fascia Vents are generally recommended as a ‘first choice’ in view of the fact that they are easier to install, mores aesthetically pleasing and will not allow the ingress of moisture when soffits are being cleaned.

VENT Systems is however currently in the design phase of a soffit strip which can easily be applied to both new build or existing buildings.

Do VENT products (RV10) perform well in strong wind areas?

VENT Systems Ridge Vent, Apron Vent and Vented Battens are BRANZ appraised for High Wind Zones. Please refer to VENTS BRANZ Appraisal 979 in our technical literature.

All other VENT Systems products have long history of use in countries with high wind zones comparable to those experienced in Australia.

Can G1275 stop rats?

No. Unfortunately rats have been known to eat through metal. In other words, if a rat wants to access a building… it will! Can the G1275 deter rats, absolutely. When faced with obstacles, rats will always seek an easier access point.

The G1275 will however prevent birds and nesting insects from accessing and nesting in roofing profiles. At the same time it is designed to never block airflow, unlike some traditional foam products.

How close would you put G700 to each other?

There are two recommended spacings for the G700 VENT Systems Circular Soffit Vent, depending on the amount of calculated airflow you need to enter the roof cavity.

To achieve For 10,000mm² per linear metre, recommended spacings are 200mm apart.

To achieve 25,000mm² per linear metre, recommended spacings are at 86mm staggered centres. Yes, this is a large amount of vents however one must remember that we are trying to achieve ‘calculated’ and ‘continuous’ airflow. Sporadically placed vents will not adequately ventilate your roof cavity.

As an alternative both the G1200N and G2500N Over Fascia vents can be used.

Can the G1200N or G2500N VENT Over Fascia Vents be retrofitted?

Both vents can be retro fitted depending on a number of factors. The G1200N being the smaller of the two vents requires only 18mm spacing between fascia and roof cladding. The G2500N being the larger of the two vents requires a 32mm spacing between fascia and roof cladding and therefore may be more difficult.

Removing the roof in its entirety and raising the roof height is definitely the easiest way to retro fit the vents. However, if the roof is in place and you are simply attempting to install the vents, the lower portion of the roof cladding will need to be lifted and the over fascia vents be positioned on top of the fascia. Securing the Over Fascia Vents is ideally achieved by fixing through the top of the vents and into the timber or metal fascia. As the roof cladding will press own on the vent when in place using the correct plastic to timber or plastic to metal adhesive will hold the Over Fascia Vents in place.

For new build installations please refer to the VENT Systems installation guide in our Resources page.

Are Vent products recyclable?
Yes. All VENT products are recyclable.